Substrate processing method and substrate processing apparatus

ABSTRACT

A substrate that includes a first film of a silicon-containing film and a second film having a second aperture formed on the first film is subjected to processing that includes: preparing the substrate; controlling a temperature of the substrate to −30° C. or less; and etching the first film through the second aperture using a plasma formed from a first process gas containing a fluorocarbon gas. By etching the first film through the second aperture, a first aperture of a tapered shape is formed in the first film such that a width of the first aperture gradually decreases toward a bottom of the first aperture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based upon and claims priority to JapanesePatent Application No. 2019-077359 filed on Apr. 15, 2019, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a substrate processing method and asubstrate processing apparatus.

BACKGROUND

As wafer processing becomes finer, wiring widths and contact holediameters formed on wafers tend to be smaller. Accordingly, plasmaetching methods have been proposed which allow etching the etch targetfilm into a finer linewidth or contact hole pattern.

For example, Patent Document 1 describes a technique for etching anorganic film layer more finely. In the technique described in PatentDocument 1, an intermediate layer of a silicon oxide film, which isformed on the organic film layer, is etched such that the size of anaperture at the bottom of the intermediate layer is smaller than thesize of the corresponding pattern of a resist layer formed on theintermediate layer. Thus, the organic film layer is more finely etchedthan the pattern of the resist layer.

However, when a mask pattern is transferred to an etching target film,if etching is performed using a process gas having a precursor causingdeposition easily, deposits adhere to the upper portion of the maskpattern, and the deposits may occlude apertures of the mask pattern.

CITATION LIST [Patent Document] [Patent Document 1] Japanese Laid-openPatent Application Publication No. 2007-005377 SUMMARY

According to one aspect of the present disclosure provides for a methodof processing a substrate that includes a first film of asilicon-containing film and a second film formed on the first film andhaving a second aperture. The method includes: preparing the substrate;controlling a temperature of the substrate to −30° C. or less; andetching the first film through the second aperture using a plasma formedfrom a first process gas containing a fluorocarbon gas. By etching thefirst film through the second aperture, a first aperture of a taperedshape is formed in the first film such that a width of the firstaperture gradually decreases toward a bottom of the first aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an example of a substrateprocessing apparatus according to an embodiment;

FIG. 2 is a view illustrating an outline of an etching process of afirst layered structure according to the embodiment;

FIG. 3 is a diagram illustrating an example of etching steps for eachlayer of the first layered structure according to the embodiment;

FIG. 4A is a diagram illustrating an example of a result of the etchingprocess according to the embodiment;

FIG. 4B is a diagram illustrating an example of a result of the etchingprocess according to a comparative example;

FIG. 5 is a diagram illustrating a relationship between an amount of H₂added in the etching process according to the present embodiment andblockage of an aperture;

FIG. 6 is a schematic diagram illustrating a relationship between gastypes used in the etching process according to the embodiment anddeposition states of deposits;

FIG. 7 is a diagram for explaining a surface reaction in the etchingprocess according to the embodiment;

FIG. 8 is a flowchart illustrating an example of a substrate processingmethod according to the embodiment;

FIGS. 9A to 9G are diagrams sequentially illustrating etching steps foreach layer of a second layered structure according to the embodiment;and

FIGS. 10A to 10C are diagrams illustrating etching steps applied torespective layers of a third layered structure according to theembodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the drawings. Note that in the drawings, elementshaving substantially identical features are given the same referencesymbols and overlapping descriptions may be omitted.

<Substrate Processing Apparatus>

A substrate processing apparatus 1 according to an embodiment will bedescribed with reference to FIG. 1. FIG. 1 is a cross-sectional diagramillustrating an example of the substrate processing apparatus 1according to the present embodiment.

The substrate processing apparatus 1 includes a processing vessel 10.The processing vessel 10 provides an inner space 10 s therein. Theprocessing vessel 10 includes a processing vessel body 12. Theprocessing vessel body 12 has a generally cylindrical shape. Theprocessing vessel body 12 may be formed of aluminum, for example. Acorrosion-resistant film is provided on an inner surface of theprocessing vessel body 12. The film may be a ceramic such as aluminumoxide, yttrium oxide and the like.

A passage 12 p is formed in the side wall of the processing vessel body12. A substrate W is conveyed between the inner space 10 s and theexterior of the processing vessel 10 through the passage 12 p. Thepassage 12 p is opened and closed by a gate valve 12 g provided alongthe side wall of the processing vessel body 12.

A support 13 is provided on the bottom of the processing vessel body 12.The support 13 is formed of an insulating material. The support 13 has agenerally cylindrical shape. The support 13 extends upward from thebottom of the processing vessel body 12 in the inner space 10 s. A stage14 is attached to an upper portion of the support 13. The stage 14 isconfigured to support the substrate W in the inner space 10 s.

The stage 14 includes a lower electrode 18 and an electrostatic chuck20. The stage 14 may further include an electrode plate 16. Theelectrode plate 16 is formed of a conductor such as aluminum, and isgenerally of a disc shape. The lower electrode 18 is provided on theelectrode plate 16. The lower electrode 18 is formed of a conductor suchas aluminum, and is generally of a disc shape. The lower electrode 18 iselectrically connected to the electrode plate 16.

The electrostatic chuck 20 is provided on the lower electrode 18. Thesubstrate W is placed on the top surface of the electrostatic chuck 20.The electrostatic chuck 20 includes a body and an electrode. The body ofthe electrostatic chuck 20 is generally of a disc shape, and is formedof a dielectric material. The electrode of the electrostatic chuck 20 isa film-like electrode, and is embedded in the body of the electrostaticchuck 20. The electrode of the electrostatic chuck 20 is connected to adirect-current (DC) power supply 20 p via a switch 20 s. When DC voltageis applied from the DC power supply 20 p to the electrode of theelectrostatic chuck 20, electrostatic attracting force is generatedbetween the electrostatic chuck 20 and the substrate W. The substrate Wis held on the electrostatic chuck 20 by the electrostatic attractiveforce.

An edge ring 25 is disposed on the periphery of the lower electrode 18to surround an edge of the substrate W. The edge ring 25 may also bereferred to as a focus ring. The edge ring 25 improves in-planeuniformity of a plasma process for the substrate W. The edge ring 25 maybe formed of silicon, silicon carbide, quartz, or the like.

A flow passage 18 f is formed in the lower electrode 18. Coolant, suchas brine, is supplied to the flow passage 18 f from a chiller unit (notillustrated) disposed outside the processing vessel 10 through a pipe 22a. The coolant supplied to the flow passage 18 f is returned to thechiller unit via the pipe 22 b. In the substrate processing apparatus 1,the temperature of the substrate W placed on the electrostatic chuck 20is controlled in accordance with heat exchange between the coolant andthe lower electrode 18. The coolant supplied from the chiller unit maynot only cool the lower electrode 18, but also function as a temperaturecontrolling medium to warm the lower electrode 18. The temperature ofthe coolant (temperature controlling medium) is adjusted by the chillerunit such that the temperature value detected by a temperature sensor(not illustrated) provided on the electrostatic chuck 20 (or the lowerelectrode 18) is maintained at a predetermined value.

The substrate processing apparatus 1 is provided with a gas supply line24. The gas supply line 24 supplies heat transmitting gas (e.g., He gas)from a heat transmitting gas supply mechanism to a gap between an uppersurface of the electrostatic chuck 20 and a bottom surface of thesubstrate W.

The substrate processing apparatus 1 further includes an upper electrode30. The upper electrode 30 is located above the stage 14. The upperelectrode 30 is supported at the top of the processing vessel body 12via a member 32. The member 32 is formed of an insulating material. Theupper electrode 30 and the member 32 occlude an upper opening of theprocessing vessel body 12.

The upper electrode 30 may include a top plate 34 and a support member36. The lower surface of the top plate 34 faces the inner space 10 s.The lower surface of the top plate 34 is one of the components thatdefines the inner space 10 s. The top plate 34 may be formed of a lowresistance conductor or semiconductor with low Joule heat generation.The top plate 34 includes multiple gas discharge holes 34 a thatpenetrate the top plate 34 in a thickness direction of the top plate 34.

The support member 36 removably supports the top plate 34. The supportmember 36 is formed of an electrically conductive material such asaluminum. Inside the support member 36 is a gas diffusion chamber 36 a.The support member 36 includes multiple gas holes 36 b extendingdownward from the gas diffusion chamber 36 a. Each of the multiple gasholes 36 b communicates with a corresponding one of the multiple gasdischarge holes 34 a. A gas inlet 36 c is formed in the support member36. The gas inlet 36 c is connected to the gas diffusion chamber 36 a. Agas supply line 38 is connected to the gas inlet 36 c.

Valves 42, flow controllers 44, and gas sources 40 are connected to thegas supply line 38. In the present embodiment, a set of the gas sources40, the valves 42, and the flow controllers 44 is referred to a gassupply section. Each of the flow controllers 44 may be a mass flowcontroller or a pressure-controlled flow controller. Each of the valves42 may be an open/close valve. Each of the gas sources 40 is connectedto the gas supply line 38 via a corresponding one of the valves 42 and acorresponding one of the flow controllers 44.

In the substrate processing apparatus 1, a removable shield 46 isprovided along a surface of the inner side wall of the processing vesselbody 12 and along a surface of the outer circumference of the support13. The shield 46 prevents reaction products from adhering to theprocessing vessel body 12. The shield 46 may be, for example,constructed by forming a corrosion-resistant film on a surface of a basematerial formed of aluminum. The corrosion resistant film may be made ofa ceramic such as yttrium oxide.

A baffle plate 48 is provided between the outer circumference of thesupport 13 and the inner side wall of the processing vessel body 12. Thebaffle plate 48 may be, for example, constructed by forming acorrosion-resistant film (such as a film made of yttrium oxide) on asurface of a base material formed of aluminum. Multiple through-holesare formed in the baffle plate 48. An exhaust port 12 e is providedbelow the baffle plate 48 and at the bottom of the processing vesselbody 12. An exhaust device 50 is connected to the exhaust port 12 e viaan exhaust pipe 52. The exhaust device 50 includes a pressure controlvalve and a vacuum pump such as a turbomolecular pump.

The substrate processing apparatus 1 includes a first radio frequencypower supply 62 and a second radio frequency power supply 64. The firstradio frequency power supply 62 is a power supply that generates firstradio frequency electric power (hereinafter referred to as “HF power”).The first radio frequency electric power has a frequency suitable forgenerating a plasma. The frequency of the first radio frequency electricpower is in the range of 27 MHz to 100 MHz, and may be, for example, 40MHz. The first radio frequency power supply 62 is connected to the lowerelectrode 18 via a matching device 66 and the electrode plate 16. Thematching device 66 includes circuitry for causing output impedance ofthe first radio frequency power supply 62 to match impedance of a load(lower electrode 18). The first radio frequency power supply 62 may beconnected to the upper electrode 30 via the matching device 66. Thefirst radio frequency power supply 62 constitutes an example of a plasmagenerator.

The second radio frequency power supply 64 is a power supply thatgenerates second radio frequency electric power (hereinafter referred toas “LF power”). The second radio frequency electric power has afrequency lower than the frequency of the first radio frequency electricpower. If a second radio frequency electric power is used in conjunctionwith the first radio frequency electric power, the second radiofrequency electric power is used as radio frequency electric power forbias voltage, to draw ions into the substrate W. The frequency of thesecond radio frequency electric power is in a range of, for example, 400kHz to 13.56 MHz, and may be 13.56 MHz for example. The second radiofrequency power supply 64 is connected to the lower electrode 18 via amatching device 68 and the electrode plate 16. The matching device 68includes circuitry for causing output impedance of the second radiofrequency power supply 64 to match the impedance of the load (lowerelectrode 18).

It should be noted that a plasma may be generated using the second radiofrequency electric power, without using the first radio frequencyelectric power. That is, only the single radio frequency electric powermay be used for generating a plasma. In this case, the frequency of thesecond radio frequency electric power may be greater than 13.56 MHz, forexample 40 MHz. Also, in this case, the second radio frequency powersupply 64 constitutes an example of the plasma generator, and thesubstrate processing apparatus 1 does not need to include the firstradio frequency power supply 62 and the matching device 66.

In the substrate processing apparatus 1, a gas is supplied from the gassupply section to the inner space 10 s to generate a plasma. Also, bythe first radio frequency electric power and/or the second radiofrequency electric power being supplied, a radio-frequency electricfield is generated between the upper electrode 30 and the lowerelectrode 18. The gas is formed into the plasma by the generatedradio-frequency electric field.

The substrate processing apparatus 1 includes a power supply 70. Thepower supply 70 is connected to the upper electrode 30. The power supply70 applies DC voltage to the upper electrode 30 to draw positive ionsthat are present in the inner space 10 s into the top plate 34. The DCvoltage applied to the upper electrode 30 is in a range equal to orgreater than −1000 V and equal to or smaller than 0 V.

The substrate processing apparatus 1 may further include a controller80. The controller 80 may be a computer including a processor, a storagedevice such as a memory, an input device, a display device, aninput/output interface of signals, and the like. The controller 80controls each part of the substrate processing apparatus 1. By using theinput device, an operator of the substrate processing apparatus 1 caninput commands to the controller 80 to manage the substrate processingapparatus 1. Also, the controller 80 can display an operating status ofthe substrate processing apparatus 1 on the display device. Further, acontrol program and recipe data are stored in the storage device. Thecontrol program is executed by the processor, which executes variousprocesses in the substrate processing apparatus 1. The processorexecuting the control program controls each part of the substrateprocessing apparatus 1, in accordance with the recipe data.

<Etching of Substrate Having First Layered Structure>

Next, an etching process of the substrate W (may also be referred to asa “wafer W”) using the above-described substrate processing apparatus 1will be described with reference to FIGS. 2 and 3. FIG. 2 is a diagramillustrating an outline of the etching process according to the presentembodiment that is applied to a first layered structure. FIG. 3 is adiagram illustrating an example of steps of etching each layer of thefirst layered structure illustrated in a diagram (a) of FIG. 2.

The first layered structure on the substrate W to be etched isillustrated in the diagram (a) of FIG. 2 and a diagram (a) of FIG. 3.The first layered structure is an example of a multi-film structureformed on the substrate W. As illustrated in the diagram (a) of FIG. 2,in the first layered structure, from the bottom, a silicon nitride film91, a silicon oxide film 92, an organic film 93, a silicon-containingantireflection film 94, and a photoresist 95 are layered on a siliconsubstrate 90. Note that the silicon nitride film 91 may or may not beprovided.

The photoresist 95, the silicon-containing antireflection film 94, andthe organic film 93 can function as masks. The photoresist 95 hasapertures 96. In the following description, the apertures 96 may bereferred to as “second apertures 96”. The second apertures 96 areregularly arranged in a plan view of the photoresist 95, and thephotoresist 95 is patterned by photolithography. The silicon-containingantireflection film 94 is etched by using the photoresist 95 as a mask,thereby forming apertures 97 (may also be referred to as “firstapertures 97”) in the silicon-containing antireflection film 94. Thesilicon-containing antireflection film 94 is an example of a first filmthat is a silicon-containing film. The photoresist 95 is an example of asecond film formed on the first film and having a second aperture.

An example of the first film, which is a silicon-containing film, may bea silicon oxide film containing an organic substance, such ashydrocarbons. Alternatively, a silicon oxynitride film, such as SiON,may be used. These films are used as an antireflection film when formingthe second apertures 96 as an exposure pattern in the photoresist 95 byphotolithography.

The organic film 93 is a spin-on carbon film formed on the silicon oxidefilm 92 by spin coating. However, the organic film 93 may be anamorphous carbon film that is deposited on the silicon oxide film 92 bychemical vapor deposition (CVD). The organic film 93, thesilicon-containing antireflection film 94, and the photoresist 95function as masks to etch the silicon oxide film 92. The etching of thesilicon oxide film 92 is made until the silicon nitride film 91 isexposed at the bottom of a recess formed by the etching.

First, the silicon-containing antireflection film 94 is etched throughthe second apertures 96 in the photoresist 95. Process conditions duringthe etching of the silicon-containing antireflection film 94 are asfollows.

<Process Conditions During Etching of the Silicon-ContainingAntireflection Film 94>

-   -   Pressure: 50 mTorr (6.67 Pa)    -   HF power: 300 W    -   LF power: 300 W    -   Gas type: CF₄, H₂    -   Substrate temperature: variable

Three types of experiments were performed by using different gases. In afirst experiment, only CF₄ was used and H₂ was not used. A secondexperiment used a mixed gas containing CF₄ and H₂ at a ratio ofCF₄:H₂=25:3. A third experiment used a mixed gas containing CF₄ and H₂at a ratio of CF₄:H₂=25:6.

It should be noted that the supplied CF₄ gas and the supplied mixed gasof CF₄ gas and H₂ gas are examples of a first process gas.Fluorine-containing gas, such as SF₆ gas or NF₃ gas may be added to theCF₄ gas.

The temperature of the substrate is controlled by the temperature of theelectrostatic chuck 20 adjusted to a predetermined temperature by thechiller unit, as heat of the electrostatic chuck 20 is transferred tothe substrate through the surface of the electrostatic chuck 20 and theheat transmitting gas. However, the substrate temperature, particularlythe temperature of the surface of the substrate facing a plasma, maybecome higher than the adjusted temperature of the electrostatic chuck20, because the substrate is exposed to the plasma generated by thefirst radio frequency electric power for plasma excitation, therebybeing irradiated with light of the plasma and being bombarded with ionsdrawn by the second radio frequency electric power for bias voltage. Thetemperature of the substrate can also be increased by radiant heat fromthe upper electrode or the side wall of the processing vessel body 12.Thus, if an actual substrate temperature can be measured during theetching process, or if a temperature difference between the adjustedtemperature of the electrostatic chuck 20 and an actual surfacetemperature of the substrate can be estimated from the processconditions, a temperature setting of the electrostatic chuck 20 may belowered to adjust the temperature of the substrate to a predeterminedtemperature range. If it is assumed that the temperature differencebetween the adjusted temperature of the electrostatic chuck 20 and theactual surface temperature of the substrate is small, such as in a casein which the first radio frequency electric power and the second radiofrequency electric power are small, the substrate temperature may beconsidered as being equal to the temperature of the electrostatic chuck20.

After the silicon-containing antireflection film 94 is etched, theorganic film 93 is etched using the silicon-containing antireflectionfilm 94 as a mask. Process conditions during etching of the organic film93 are as follows.

<Process Conditions During Etching of the Organic Film 93>

-   -   Pressure: 15 mTorr (2.00 Pa)    -   HF Power: 100 W    -   LF Power: 750 W    -   Gas type: N₂, H₂    -   Substrate temperature: variable

In the following description, “extremely low temperature” means atemperature equal to or less than −30° C., and “ordinary temperature”means a temperature of 0° C. or more and in the vicinity of a roomtemperature. Also, the supplied mixed gas of N₂ gas and H₂ gas is anexample of a second process gas. Other examples of the second processgas may include O₂ gas, a mixture of O₂ gas and CO₂ gas, a mixture of O₂gas and SO₂ gas, and a mixture of O₂ gas and COS gas.

The etching of the organic film 93 is not required to be carried out atan extremely low temperature, but may be carried out at an ordinarytemperature. However, an extremely low temperature environmentfacilitates mass production. Also, an effect of shrinking criticaldimension (CD) can be obtained in etching under the extremely lowtemperature environment. Therefore, it is preferable to control asubstrate temperature at the extremely low temperature. The type of gasused to etch the organic film 93 is not limited to the mixed gas of N₂gas and H₂ gas. A mixture of O₂ gas and CO₂ gas, a mixture of O₂ gas andSO₂ gas, a mixture of O₂ gas and COS gas, or the like, may be used.

After etching the organic film 93, the silicon oxide film 92 is etchedusing the organic film 93 as a mask. Process conditions during theetching of the silicon oxide film 92 are as follows.

<Process Conditions During Etching of Silicon Oxide Film 92>

-   -   Pressure: 25 mTorr (3.33 Pa)    -   HF power: 0 W    -   LF power: 800 W    -   Gas type: CF₄, H₂    -   Substrate temperature: −45° C.

The etching of the silicon oxide film 92 need not be carried out at anextremely low temperature, but may be carried out at an ordinarytemperature. However, as the reaction product generated during etchingis adhered to the inner wall of the etched silicon oxide film 92 underan extremely low temperature environment, an effect of protecting theinner wall of the etched silicon oxide film 92 is obtained. Thus,etching of the sidewall of an etched hole (or recess) formed in thesilicon oxide film 92 can be suppressed. Therefore, it is preferable tocontrol the substrate temperature to extremely low temperatures. Also,it is easy to maintain an etching profile of the silicon oxide film 92in a vertical shape. Furthermore, it is preferable to perform theoperation at an extremely low temperature in order to obtain an effectof shrinking an etching profile. The type of gas used in the etching ofthe silicon oxide film 92 is not limited to the above-mentioned gas, anda mixture of C₄F₆ gas, O₂ gas and Ar gas, a mixture of C₄F₈ gas, O₂ gasand Ar gas, or the like may be used.

An example of a result of etching the silicon-containing antireflectionfilm 94, the organic film 93, and the silicon oxide film 92 in sequenceaccording to the above-described process conditions is illustrated in adiagram (b) of FIG. 2. The horizontal axis of the diagram (b) of FIG. 2indicates the substrate temperature during etching of thesilicon-containing antireflection film 94 and the organic film 93. Thevertical axis of the diagram (b) of FIG. 2 indicates a CD value(hereinafter referred to as a “TOP CD value”) representing a width of anaperture at an upper end formed in the silicon oxide film 92, after thesilicon oxide film 92 is etched until the silicon nitride film 91 isexposed and the organic film 93 is further removed by asking, which isillustrated in a frame of the diagram (a) of FIG. 2.

The curve A illustrated in the diagram (b) of FIG. 2 represents the TOPCD value in a case in which only CF₄ gas is supplied and no H₂ gas isadded during etching of the silicon-containing antireflection film 94.The curve B represents the TOP CD value in a case in which H₂ gas isadded to the CF₄ gas in a ratio of CF₄:H₂=25:3 during etching of thesilicon-containing antireflection film 94. The curve C represents theTOP CD value in a case in which H₂ gas is added to the CF₄ gas in aratio of CF₄:H₂=25:6 during etching of the silicon-containingantireflection film 94.

According to the result illustrated in the diagram (b) of FIG. 2, the CDvalue became approximately 13 nm or less when the substrate temperaturewas set to −30° C. or less, which corresponds to a region surrounded bya frame S shown with the dashed line (hereinafter, this temperaturecondition may be referred to as an “extremely low temperaturecondition”), and the TOP CD value shrank more as compared to a case inwhich etching is performed at an ordinary temperature. Specifically, asillustrated in the diagram (a) of FIG. 2, in a case of the curve A inwhich H₂ was not added to CF₄, the TOP CD value was 13.5 nm or less,while a CD value (width) of the second aperture 96 of the photoresist 95was 28 nm. In other words, by supplying the gas containing CF₄ gas(hereinafter, referred to as the “first process gas”) during etching ofthe silicon-containing antireflection film 94 under the extremely lowtemperature condition, the TOP CD value could be shrunk.

Furthermore, in a case of the curve B in which H₂ was added to CF₄, theTOP CD value became less than 10 nm under the extremely low temperaturecondition. From the above, it has been found that if H₂ is added to CF₄during the etching process of the silicon-containing antireflection film94, the TOP CD value can be shrunk significantly compared to a case inwhich H₂ is not added to CF₄.

Accordingly, in a step of etching the silicon-containing antireflectionfilm 94 illustrated in a diagram (a) and a diagram (b) of FIG. 3, aplasma formed from the first process gas containing CF₄ gas is used, andthe substrate temperature is controlled to be equal to or less than −30°C. Then, the silicon-containing antireflection film 94 exposed from thesecond aperture 96 is etched.

Accordingly, as illustrated in the diagram (b) of FIG. 3, across-section of the first aperture 97 in the silicon-containingantireflection film 94 is formed into a tapered shape, such that a size(width) of a hole (first aperture 97) formed in the silicon-containingantireflection film 94 gradually decreases toward a bottom of the hole(first aperture 97) in a cross-sectional view. That is, a cross-sectionof the first aperture 97 is formed into a tapered shape such that a size(width) of the first aperture 97 on a side opposite the photoresist 95is smaller than a size (width) of the first aperture 97 on a side of thephotoresist 95. This allows the TOP CD value of the silicon oxide film92 to be less than half of the CD value of the second aperture 96 of thephotoresist 95 when etching the silicon oxide film 92, thereby forming asmall contact in the shrunken recess. Further, by supplying the firstprocess gas with H₂ gas, a tapered angle can be made to be greater (theslope of the cross section of the first aperture 97 in thesilicon-containing antireflection film 94 can be made to be gentler) ascompared to a case in which H₂ is not added, thereby increasing theeffect of shrinking the TOP CD value.

In addition, as illustrated in a diagram (c) of FIG. 3, the firstaperture 97 of the silicon-containing antireflection film 94 was notclogged in both cases in which H₂ was not added to CF₄ during etching ofthe silicon-containing antireflection film 94 and in which H₂ was addedto CF₄ in a ratio of CF₄:H₂=25:3. Further, in a step of etching thesilicon oxide film 92 through the aperture 98 formed in the organic film93, as illustrated in a diagram (d) of FIG. 3, the silicon oxide film 92could be etched until the silicon nitride film 91 was exposed withoutthe aperture 98 becoming clogged. However, in a case in which H₂ wasadded to CF₄ in a ratio of CF₄:H₂=25:6 under the extremely lowtemperature condition, the CD value significantly decreased, and anaperture was not formed on the silicon oxide film 92. Therefore, the CDvalue under the extremely low temperature condition could not beindicated in the diagram (b) of FIG. 2.

FIG. 4A is a diagram illustrating an example of a result of the etchingprocess according to the present embodiment, and FIG. 4B is a diagramillustrating an example of a result of an etching process according to acomparative example. FIG. 4A illustrates an example of a top view ofholes 99 formed in the silicon oxide film 92 of the first layeredstructure, which illustrates a state after each etching step accordingto the present embodiment has been performed and the organic film 93illustrated in the diagram (d) of FIG. 3 has been removed by ashing.FIG. 4B illustrates an example of a top view of holes 109 formed in asilicon oxide film 92 of the first layered structure by performing eachetching step according to the comparative example.

In etching the silicon-containing antireflection film 94 of the firstlayered structure, experiments were performed by changing the substratetemperature and by changing the process gas. Also, with respect to thesubstrate temperature, etching was performed in cases of −45° C., 0° C.,and 30° C. The etching process of the silicon-containing antireflectionfilm 94 of the first layered structure according to the comparativeexample differs from that according to the present embodiment in that amixed gas of CHF₃ gas and CF₄ gas was supplied in the comparativeexample, while CF₄ gas or a mixed gas of CF₄ gas and H₂ gas was suppliedin the present embodiment. The process conditions in the etching processof the organic film 93 and the silicon oxide film 92 according to thecomparative example are the same as those according to the presentembodiment.

As a result of the etching process according to the comparative example,in a case in which the substrate temperature is 0° C. and 30° C.,although the TOP CD value of the silicon oxide film 92 was shrunk toapproximately 10 nm, openings of the holes 109 are not regularlyarranged, and some holes 109 are not formed on the silicon oxide film 92(in the following description, a point on the silicon oxide film 92 inwhich a hole 109 was to be formed but in which the hole 109 could not beformed as a result of etching is referred to as a “blind”). That is, thesilicon oxide film 92 is not etched in the same pattern as the patternof the second apertures in the photoresist 95. It is assumed that thisis because some apertures (in the silicon-containing antireflection film94 or in the photoresist 95) became clogged with reaction productsproduced during etching of the silicon-containing antireflection film94. Also, in a case in which the substrate temperature was −45° C., anamount of reaction products produced during etching was furtherincreased, and no holes 109 were formed on the silicon oxide film 92.

On the other hand, as a result of performing the etching processaccording to the present embodiment, in cases in which the substratetemperature is 0° C. and 30° C., openings of the holes 99 were arrangedregularly and no blinds were seen. However, even if H₂ gas was added toCF₄ gas, the TOP CD value did not fall below 10 nm, and shrinkage of theTOP CD value was limited. Conversely, in a case in which the substratetemperature was −45° C., the silicon oxide film 92 could be etched inthe same pattern as the pattern of the second apertures in thephotoresist 95 while avoiding generation of blinds and reducing the TOPCD value of the silicon oxide film 92 to less than 10 nm.

Thus, in order to shrink apertures in the silicon-containingantireflection film 94 without occluding the second aperture 96 of thephotoresist 95, it is necessary to control the substrate temperature toan extremely low temperature of −30° C. or less in the etching process.Meanwhile, in the step of etching the organic film 93 and the step ofetching the silicon oxide film 92, it is not necessary to set thesubstrate temperature to the extremely low temperature of −30° C. orless. The substrate temperature may be set to −30° C. or higher.However, as described above, it is preferable to control the substratetemperature to the extremely low temperature even in the step of etchingthe organic film 93 and in the step of etching the silicon oxide film92.

<Amount of H₂ Added>

Next, the amount of H₂ gas to be added will be described with referenceto FIG. 5. FIG. 5 is a diagram illustrating the relationship between theamount of H₂ added in the etching process according to the presentembodiment and blockage of an upper end portion of an aperture. Thehorizontal axis of FIG. 5 indicates the substrate temperature, and thevertical axis of FIG. 5 indicates a flow ratio of H₂ gas with respect toa total flow of a mixed gas of CF₄ gas and H₂ gas during the etchingprocess of the silicon-containing antireflection film 94.

The curve E in FIG. 5 represents a case in which CD is shrunk and inwhich no blind is present, that is, the curve E represents a case inwhich the holes 99 having shrunken CD are formed and are regularlyarranged on the silicon oxide film 92. Meanwhile, a curve F in FIG. 5represents a case in which CD is shrunk but in which blinds are present.That is, the curve F represents a case in which the holes 99 havingshrunken CD are formed but are irregularly arranged on the silicon oxidefilm 92, such that one or more holes 99 is not formed on the siliconoxide film 92 or no holes 99 are formed on the silicon oxide film 92.

According to the results illustrated in FIG. 5, if H₂ gas is added tothe first process gas such that an amount of H₂ gas contained in thefirst process gas satisfies the following formula (1), the effect ofshrinking CD is obtained, and regularly arranged holes 99, similar tothe pattern of the second apertures in the photoresist 95, can be formedin the silicon oxide film 92, without causing a portion in which theholes 99 could not be formed.

0≤y≤0.0078x ²−0.3938x+11.877  (1)

where y is a partial pressure percentage (%) of H₂ gas, which is a ratioof a flow rate of H₂ gas with respect to a total flow rate of a mixedgas of CF₄ gas and H₂ gas (total flow rate of the first process gas),and x is the substrate temperature.

<Relationship Between Gas Type and Deposition State>

Next, the relationship between gas types used in the etching processaccording to the present embodiment and deposition states of deposits inthe etching process will be described with reference to FIGS. 6 and 7.FIG. 6 is a schematic diagram illustrating the relationship between gastypes used in the etching process according to the present embodimentand deposition states of deposits. FIG. 7 is a diagram for explaining asurface reaction in the etching process according to the presentembodiment.

The deposited states of reaction products produced by etching when CF₄gas was used is illustrated on an upper row of FIG. 6, and the depositedstates of reaction products produced by etching when CHF₃ gas was usedis illustrated on a lower row of FIG. 6. Both rows illustrate a case inwhich etching was performed at the extremely low temperature of −45° C.,and a case in which etching was performed at an ordinary temperature of0° C.

With respect to deposition property of CH_(x)F_(y) gases, it isgenerally considered that deposition property increases in an order ofCF₄, CHF₃, CH₂F₂, and CH₃F. This order is determined by a manner ofdissociation of each molecule, and by sticking coefficients of radicalsgenerated by dissociation, with respect to a deposition target film.

For example, energy required to generate CF_(x) radicals fromdissociation of CF₄ and CHF₃ gases is as follows.

Generation of CF radical, CF₂ radical, and CF₃ radical from CF₄ gasrequires 22 eV, 19 eV, and 14.6 eV, respectively. Meanwhile, generationof CF radical, CF₂ radical, and CF₃ radical from CHF₃ gas requires 17eV, 14 eV, and 13.8 eV, respectively. In other words, under conditionswhere the same HF power and LF power are applied, the ratio of CFradicals contained in radicals generated from CF₄ gas is smaller thanthe ratio of CF radicals contained in radicals generated from CHF₃ gas.

Therefore, the ratio of CF radicals generated when CHF₃ gas is used ishigher than the ratio of CF radicals generated when CF₄ gas is used.Because sticking probability of CF radicals is an order of magnitudegreater than that of CF₂ and CF₃ radicals, deposits 110 that adhere toan upper portion of the film are more likely to be formed in a case inwhich CHF₃ gas is used at an ordinary temperature, as illustrated in thelower row of FIG. 6. Under an extremely low temperature condition, asthe amount of reaction product further increases, the risk of occurrenceof blockage (clogging) increases by increasing an amount of the deposits110 at the upper portion of the film. Conversely, in a case in which CF₄gas is used, because the ratio of CF radicals is lower than that in acase in which CHF₃ gas is used, the deposits 110 that adhere to theupper portion of the film are less likely to be formed, and clogging isless likely to occur.

Thus, because CF₄ gas has a low sticking coefficient, only radicals thatdo not contribute to deposition are generated in the plasma when CF₄ gasis used at an ordinary temperature. Therefore, as illustrated in theupper row of FIG. 6, when CF₄ gas is used at an ordinary temperature,little or no reaction products adhere to the film. In contrast, in acase in which CF₄ gas is used under an extremely low temperaturecondition of −45° C., deposition of reaction products is started, anddeposits 110 are thinly deposited on the inner wall of the secondaperture 96 and on the upper portion of the film, in a conformal manner.In this case, a gas having a low sticking coefficient, such as CF₄ gas,is less likely to adhere to the upper portion of the film, and tends toadhere to the bottom. Thus, clogging is unlikely to occur.

As described above, because the deposition property of reaction productsproduced from a single gas of CF₄ gas is small, in the etching of thesilicon-containing antireflection film 94 according to the presentembodiment, it is preferable to add H₂ gas to CF₄ gas in order toimprove deposition property. This allows the mixed gas of CF₄ gas and H₂gas to have a property similar to that of CHF₃ gas, so that deposits 110adhere under an ordinary temperature condition, similar to the caseillustrated in the lower row of FIG. 6 in which etching is performedusing CHF₃ gas. In addition, under an extremely low temperaturecondition, an amount of deposits 110 increases.

However, if an amount of H₂ gas to be added is too high under theextremely low temperature condition, the likelihood that clogging wouldoccur becomes high, as the curve F illustrated in FIG. 5 indicates. As aresult, the risk of occurrence of blockage of the hole is increased, asillustrated in the diagram at the lower row of the left column of FIG.6, in which an opening of the hole is clogged with the deposits 110.

Next, the deposits 110 deposited on the sidewall of a hole formed in thesilicon-containing antireflection film 94 will be described withreference to FIG. 7. A hole formed in the silicon-containingantireflection film 94 illustrated in FIG. 7 is tapering, as thedeposits 110 such as reaction products produced in etching are depositedon the side surface of the hole. More specifically, the deposits 110illustrated in FIG. 7 include reaction products generated duringetching, and include radicals contained in the plasma. The deposition ofthe two materials promotes tapered etching that forms a cross-sectionalshape of the hole in the silicon-containing antireflection film 94 intoa reversed trapezoidal shape. However, tapered etching is promoted in acase in which the above-mentioned two materials (reaction products andradicals) are deposited on the silicon-containing antireflection film94, but is not promoted in a case in which the two materials volatilize.Whether the materials are deposited on the silicon-containingantireflection film 94 or volatilize is determined by vapor pressure ofeach gas contributing to the etching, and the vapor pressure depends ontemperature.

When a plasma is generated from the first process gas containing CF₄gas, CF₂* (radical) or CF₂ ⁺ (ion) in the plasma promotes etching of thesilicon-containing antireflection film 94. The etching is represented bythe following chemical reaction formula.

SiO₂+2CF₂→SiF₄+2CO

SiO—R+CF₂→SiF_(x)—R+CO

where SiO—R is an example of a silicon-containing film containingorganic matter, and SiF_(x)—R is an example of a reaction product whenthe silicon-containing film containing organic matter is etched.

As a result of the above-described chemical reactions, the reactionproduct SiF_(x)—R adheres to the sidewall to form the deposits 110.According to the vapor pressure curve of SiF_(x)—R, SiF_(x)—Rvolatilizes at an ordinary temperature as illustrated in a right columnof FIG. 7, whereas at an extremely low temperature, SiF_(x)—R deposits,as illustrated in a left column of FIG. 7. SiF₄ and CO volatilize atboth the ordinary temperature and the extremely low temperature.

Thus, in a case in which the first process gas containing CF₄ gas issupplied to etch the silicon-containing antireflection film 94, anextremely low temperature of −30° C. or less is required in order toform a tapered hole in the silicon-containing antireflection film 94. Bysupplying the first process gas containing CF₄ gas under the extremelylow temperature condition, the deposits 110 can be deposited on thesidewall of the hole formed in the silicon-containing antireflectionfilm 94.

A case in which the first process gas supplied in the etching process ofthe silicon-containing antireflection film 94 is CF₄ gas or a mixture ofCF₄ gas and H₂ gas is described above. However, the first process gas isnot limited thereto, as long as the first process gas containsfluorocarbon gas. Further, the first process gas is preferably a mixedgas including fluorocarbon gas and hydrogen gas.

The fluorocarbon gas may be C_(x)F_(y) gas that satisfies y/x>3. Thefluorocarbon gas is dissociated to multiple types of precursors by aplasma. Preferably, the fluorocarbon gas is a gas in which an amount ofCF₂ produced as one of the precursors is greater than amounts of theother precursors. The fluorocarbon gas may be any of C₂F₄, C₃F₄, andC₂F₆ gases, or may be CF₄ gas.

In the present embodiment, a silicon-containing antireflection film 94is described as an example of the first film that is asilicon-containing film, but the first film is not limited thereto. Thefirst film may further contain organic matter, or may be an organicsilicon oxide film.

<Etching Process>

A substrate processing method including the aforementioned etchingprocess according to the present embodiment will be described withreference to FIG. 8. FIG. 8 is a flowchart illustrating an example ofthe substrate processing method including the etching process accordingto the present embodiment. The present process is controlled by thecontroller 80.

First, the controller 80 prepares a wafer (substrate) W on which thesilicon oxide film 92 as an example of a film to be etched (fourthfilm), the organic film 93 as an example of a third film, thesilicon-containing antireflection film 94 as an example of a first film,and the photoresist 95 as an example of a second film are formed insequence from the bottom. That is, the above-described wafer W isprepared by loading the wafer W into the processing vessel 10, and byholding the wafer W with the electrostatic chuck 20 (step S1). Thesecond film (photoresist 95), the first film (silicon-containingantireflection film 94), and the third film (organic film 93) functionas an etching mask.

Next, the controller 80 sets a temperature of the wafer W to −30° C. orless (step S2). The temperature of the wafer (wafer temperature) is setto a predetermined temperature of −30° C. or less by controlling atemperature of the coolant that is supplied from the chiller unitthrough the pipes 22 a and 22 b and that flows through the flow passage18 f illustrated in FIG. 1.

Next, the controller 80 supplies a mixture of CF₄ gas and H₂ gas intothe processing vessel 10 (step S3). The flow rate of H₂ gas isdetermined by the above-described formula (1). Subsequently, thecontroller 80 applies HF power and LF power to the lower electrode 18,to etch the first film through the second aperture 96 of the second filmby a plasma generated by the plasma generator (step S4). In the presentembodiment, the silicon-containing antireflection film 94 is etchedthrough the second aperture 96 of the photoresist 95 such that an etchedportion is formed into a tapered shape.

Next, after the etching of the first film is completed, the controller80 supplies a mixture of N₂ gas and H₂ gas into the processing vessel 10(step S5).

Next, the controller 80 applies HF power and LF power to the lowerelectrode 18, to etch the third film through the first aperture 97formed in the first film by a plasma generated by the plasma generator(step S6). In the present embodiment, the organic film 93 is etchedthrough the first aperture 97 formed in the silicon-containingantireflection film 94.

Next, after the etching of the third film is completed, the controller80 supplies a mixture of CF₄ gas and H₂ gas into the processing vessel10 (step S7). Then, the controller 80 applies HF power and LF power tothe lower electrode 18, to etch the fourth film through the aperture 98formed in the third film by the plasma generated by the plasma generator(step S8). In the present embodiment, the silicon oxide film 92, whichis an undercoat film, is etched through the aperture 98 formed in theorganic film 93.

Next, the controller 80 performs aching of the third film (step S9).This removes the organic film 93 that has served as a mask in etchingthe silicon oxide film 92. Subsequently, a metal is embedded in a holeformed in the silicon oxide film 92 (step S10). Because the metal isembedded in the hole whose CD value is shrunk by the first aperture 97in the silicon-containing antireflection film 94, a small contact havinga CD value less than 10 nm, such as approximately 6 nm, can be formed.

<Etching of Substrate Having Second Layered Structure>

Next, an example in which a substrate processing method including theetching process according to the present embodiment is applied to asubstrate W having a second layered structure will be described withreference to FIGS. 9A to 9G. FIGS. 9A to 9G are diagrams sequentiallyillustrating etching steps for each layer of the second layeredstructure according to the present embodiment.

The etching process according to the present embodiment is applied tothe substrate W having the second layered structure. FIGS. 9B to 9Fillustrate respective steps of the etching process according to thepresent embodiment. After the etching process, the step of embedding ametal wire into the shrunken hole formed by the etching process isperformed. FIG. 9G illustrates a state of the wafer W to which all thesteps of the substrate processing method, including the etching processaccording to the present embodiment, are applied.

The etching process illustrated in FIGS. 9B to 9F will be described indetail. As illustrated in FIG. 9B, an impurity layer 101 is formed in asilicon substrate 100 of the second layered structure. Also, on thesilicon substrate 100, a gate 102 is formed adjacent to the impuritylayer 101. The impurity layer 101 and the gate 102 are coated with asilicon nitride film 103 that functions as a protective film. On thesilicon nitride film 103, a silicon oxide film 104 b, a silicon nitridefilm 107, and a silicon oxide film 104 a are formed in sequence. Thesilicon nitride film 107 is an intermediate layer and is insertedbetween the silicon oxide film 104 b and the silicon oxide film 104 a.On the silicon oxide film 104 a, a mask layer 106 is formed. A secondaperture 105 is formed in the top layer in the mask layer 106.

In the initial state of the second layered structure illustrated in FIG.9B, the silicon nitride film 107 is an example of a first film that is asilicon-containing film. A set of the silicon oxide film 104 a and themask layer 106 is an example of a second film that is formed on thefirst film and includes the second aperture 105. The silicon oxide film104 b under the silicon nitride film 107 is an example of a third filmformed under the first film.

In the case of the second layered structure, when the substrateprocessing method according to the present embodiment illustrated inFIG. 8 is started, the controller 80 prepares the wafer W having thefirst to third films of the second layered structure. Next, asillustrated in FIGS. 9C and 9D, the controller 80 supplies a mixture ofN₂ gas and H₂ gas to etch the mask layer 106 through the second aperture105, then supplies a mixture of CF₄ gas and H₂ gas to etch the siliconoxide film 104 a. Next, the silicon nitride film 107 is etched such thata cross section of a hole formed in the silicon nitride film 107 becomesa tapered shape.

In the step of tapered etching of the silicon nitride film 107, thecontroller 80 sets the temperature of the wafer W to −20° C. or less.Also, the controller 80 then supplies a mixture of CF₄ gas and H₂ gasinto the processing vessel 10, and applies HF power and LF power to thelower electrode 18.

The controller 80 then etches the silicon nitride film 107 with a plasmagenerated by the plasma generator. In the etching step, the chemicalreaction of SiN (silicon nitride film 107) with the supplied mixed gasof CF₄ and H₂ results in a reaction product of ammonium fluorosilicate((NH₄)₂SiF₆) forming the deposits 110 to promote tapered etching. Inthis manner, a silicon nitride film 107 may be formed at a locationwhere tapered etching should be promoted to shrink the CD value.

Next, as illustrated in FIG. 9E, the controller 80 supplies a mixture ofCF₄ gas and H₂ gas, to etch the silicon oxide film 104 b through a firstaperture formed in the silicon nitride film 107 having a tapered shape,until the silicon nitride film 103 is exposed. At this time, it ispreferable to control the wafer temperature to −30° C. or less. Byetching the silicon oxide film 104 b with a plasma formed from the mixedgas of CF₄ and H₂ while the wafer W is cooled to −30° C. or less, a holeof vertical shape can be formed in the silicon oxide film 104 b. Thisallows a predetermined distance to be maintained between the gate 102and the hole. The mixed gas of CF₄ gas and H₂ gas supplied in the stepof etching the silicon oxide film 104 b is an example of a secondprocess gas. Other examples of the second process gas include a mixtureof C₄F₈ gas, O₂ gas, and Ar gas, and a mixture of C₄F₆ gas, O₂ gas, andAr gas. Subsequently, the controller 80 supplies a mixture of CH₂F₂ gas,O₂ gas, and Ar gas, to etch the silicon nitride film 103 until theimpurity layer 101 is exposed.

Next, as illustrated in FIG. 9F, the controller 80 supplies O₂ gas or amixture of N₂ gas and H₂ gas, to remove the mask layer 106 by ashing.Next, as illustrated in FIG. 9G, the controller 80 embeds metal in theetched hole to form a wiring layer 111. The step of removing the masklayer 106 may be performed by a device different from an apparatus(substrate processing apparatus 1) that performs etching. For example,the step of removing the mask layer 106 may be performed by ahigh-temperature plasma ashing device. Alternatively, the mask layer 106may be removed by wet cleaning.

As illustrated in FIG. 9G, with respect to the hole formed by performingthe etching process according to the present embodiment, CD of the lowerportion of the hole is smaller than CD of the upper portion of the hole.That is, the lower portion of the hole is shrunk in the etching process.This ensures a distance Q between the gate 102 and the hole.

According to the substrate processing method including theabove-described etching process, CD of the upper end of the etched holeis greater than CD of the hole near the gate 102. The CD at the upperend of the hole is limited by adjacent wiring.

For example, suppose a case of etching the silicon oxide films 104 a and104 b under the same process condition as that in the etching of thesilicon nitride film 107, to perform tapered etching of the siliconoxide films 104 a and 104 b. As this increases a tapered portion of thehole as illustrated in FIG. 9A, a distance between the gate 102 and thehole may not be able to secured.

Thus, in the etching process according to the present embodiment,tapered etching is applied to only the silicon nitride film 107, whichis an intermediate layer, using a plasma in which hydrogen and fluorineare present, under an extremely low temperature condition of −20° C. orless. This creates ammonium fluorosilicate during the etching of thesilicon nitride film 107, and ammonium fluorosilicate adheres to thesurface of the silicon nitride film 107 to form the deposits 110. As aresult, a hole formed in the silicon nitride film 107 can be etched intoa tapered shape. In the subsequent etching steps, process conditions arechanged so that an etching profile of a hole formed by the subsequentetching steps becomes a vertical shape.

As described above, if the silicon nitride film 107 as the intermediatelayer is etched while causing ammonium fluorosilicate to be deposited onan etched surface of the silicon nitride film 107, in order to form anetching profile into a tapered shape, the distance Q between the gate102 and the hole can be controlled to be a predetermined distance ormore, as illustrated in FIG. 9G.

In the above description, although a silicon nitride film is used as theintermediate layer of the second layered structure, the intermediatelayer is not limited thereto if ammonium fluorosilicate is generatedduring etching of the intermediate layer. For example, a silicon filmcontaining nitrogen, such as a silicon oxide film with SiON, can beexpected to induce the same effect.

<Etching of Substrate Having Third Layered Structure>

Next, an example in which the substrate processing method including theetching process according to the present embodiment is applied to awafer W having a third layered structure will be described withreference to FIGS. 10A to 10C. FIGS. 10A to 10C are diagramsillustrating etching steps applied to respective layers of the thirdlayered structure according to the present embodiment.

As illustrated in FIG. 10A, in the third layered structure, a gate 120and a silicon nitride film 121 as a protective film covering the gate120 are formed at the bottom of a low-k (low-permittivity) film 122. InFIGS. 10A to 10C, although the low-k film 122 includes three low-k films122 a, 122 b, and 122 c, the low-k films 122 a, 122 b, and 122 c aremade of identical material and the low-k film 122 is substantially asingle film. However, for convenience of description, the low-k film 122will be described as a set of three films (low-k films 122 a, 122 b, and122 c). The low-k film 122 b is an example of a first film that isetched into a tapered shape. The low-k film 122 a is an example of asecond film having a second aperture 124. The low-k film 122 c is anexample of a third film that becomes an undercoat film of the firstfilm. A mask 123 is formed on the upper surface of the low-k film 122 a.

Also, when etching the third layered structure, the controller 80supplies a mixture of C₄F₈ gas, Ar gas, and N₂ gas to etch the low-kfilm 122 a. Next, the controller 80 supplies a mixture of CF₄ gas and H₂gas only during an etching step of the low-k film 122 b, and the low-kfilm 122 b is etched by setting a wafer temperature to an extremely lowtemperature of −30° C. or less, and by applying HF power and LF power.This allows the low-k film 122 b to be etched in a tapered shape, anddeposits 110 can be deposited during etching, as illustrated in FIG.10B. Thus, CD of the lower end (bottom) of a hole formed in the low-kfilm 122 b can be made to be less than that of the upper end of thehole. Next, the controller 80 supplies a mixture of C₄F₈ gas, Ar gas,and N₂ gas again to etch the low-k film 122 c. This causes the low-kfilm 122 c to be etched vertically, allowing the distance P between thegate 120 and the hole to be equal to or greater than a predeterminedvalue, as illustrated in FIG. 10C. The mixture of C₄F₈ gas, Ar gas, andN₂ gas supplied when the low-k film 122 c is etched is an example of asecond process gas.

As described above, according to the etching method of the presentembodiment, with respect to the first to third layered structures, CD ofthe aperture formed in the film by etching can be reduced withoutclogging the aperture.

The first film to which the tapered etching is applied may be a lowdielectric constant film such as the low-k film 122 of FIGS. 10A to 10C,or an antireflection film such as the silicon-containing antireflectionfilm 94 of FIGS. 2 and 3. The first film may also contain nitrogen, likethe silicon nitride film 107 of FIG. 9B. The first film may be a siliconnitride film or a silicon oxynitride film.

When etching the first film, a temperature of the substrate (wafer),which is set to an extremely low temperature, may be −30° C. or less.The lower limit of the temperature is not particularly limited, but maybe, for example, equal to or greater than −60° C. due to limitations ofa configuration of the substrate processing apparatus.

During the step of etching the third film formed under the first filmthrough the first aperture formed in the first film after the step ofetching the first film, it is preferable to control the wafertemperature to −30° C. or less. However, the temperature is not limitedthereto.

In the step of etching the third film, the third film may be etchedusing a plasma formed from the second process gas, through the firstaperture.

The temperature of the wafer (substrate) during the step of etching thethird film may be equal to the temperature of the wafer during the stepof etching the first film (first temperature), or may be different.

When the first film is etched into the tapered shape, V_(DC) (self-bias)may be 2000 V for example, from the perspective of control.

The substrate processing method and the substrate processing apparatusaccording to the embodiment disclosed herein are to be consideredexemplary in all respects and not limiting. The above embodiments may bemodified and enhanced in various forms without departing from theappended claims and spirit thereof. Matters described in the aboveembodiments may take other configurations to an extent not inconsistent,and may be combined to an extent not inconsistent.

The substrate processing apparatus according to the present disclosureis applicable to any type of substrate processing apparatus, includingan atomic layer deposition (ALD) apparatus, a capacitively coupledplasma (CCP) type processing apparatus, an inductively coupled plasma(ICP) type processing apparatus, a processing apparatus using a radialline slot antenna (RLSA), an electron cyclotron resonance plasma (ECR)type processing apparatus, and a helicon wave plasma (HWP) typeprocessing apparatus.

What is claimed is:
 1. A method of processing a substrate comprising:preparing the substrate including a first film of a silicon-containingfilm and a second film in which a second aperture is formed, the secondfilm being formed on the first film; maintaining a temperature of thesubstrate to −30° C. or less; and etching the first film through thesecond aperture using a plasma formed from a first process gascontaining a fluorocarbon gas, to form a first aperture of a taperedshape in the first film such that a width of the first aperturegradually decreases toward a bottom of the first aperture.
 2. The methodaccording to claim 1, wherein the first process gas contains H₂ gas. 3.The method according to claim 2, wherein an amount of the H₂ gascontained in the first process gas satisfies a condition of0≤y≤0.0078x ²−0.3938x+11.877, wherein y is a partial pressure percentage(%) of the H₂ gas contained in the first process gas, and x is atemperature (° C.) of the substrate.
 4. The method according to claim 1,wherein the fluorocarbon gas is C_(x)F_(y) gas, where relationshipbetween x and y satisfies y/x>3.
 5. The method according to claim 4,wherein the fluorocarbon gas is CF₄ gas.
 6. The method according toclaim 1, wherein the fluorocarbon gas is dissociated to multiple typesof precursors by a plasma, and an amount of CF₂ of the precursors isgreater than amounts of other precursors.
 7. The method according toclaim 6, wherein the fluorocarbon gas is any one of C₂F₄ gas, C₃F₄ gas,and C₂F₆ gas.
 8. The method according to claim 1, wherein the first filmcontains organic matter.
 9. The method according to claim 8, wherein thefirst film is an organic silicon oxide film.
 10. The method according toclaim 1, wherein the first film is an antireflection film or a lowdielectric constant film.
 11. The method according to claim 1, whereinthe first film contains nitrogen.
 12. The method according to claim 1,wherein the first film is a silicon nitride film or a silicon oxynitridefilm.
 13. The method according to claim 1, wherein the substrate furtherincludes a third film formed under the first film; and the methodfurther comprises etching the third film through the first aperture,after the etching of the first film.
 14. The method according to claim13, wherein the etching of the third film includes controlling thetemperature of the substrate to −30° C. or less.
 15. The methodaccording to claim 13, wherein the third film is etched using a plasmaformed from a second process gas.
 16. A substrate processing apparatuscomprising: a processing vessel; a plasma generator configured to form aplasma in the processing vessel; and a controller configured to performa process including preparing a substrate including a first film of asilicon-containing film and a second film in which a second aperture isformed, the second film being formed on the first film; maintaining atemperature of the substrate to −30° C. or less; and etching the firstfilm through the second aperture using a plasma formed from a firstprocess gas containing a fluorocarbon gas, to form a first aperture of atapered shape in the first film such that a width of the first aperturegradually decreases toward a bottom of the first aperture.